The O stock used metadyne control with the regen being part of a
closed loop control system - IIRC (need to check "Steam to
Silver"!) there was no regen to the rails, as such.
The Metadyne system was capable of and intended to provide regenerative
braking. The problem was that the power supply was never modified to
take regeneration and the system wasn't reliable enough, being
electro-mechanical.
